This invention relates generally to a machine for piercing a taphole for a shaft furnace. More particularly, this invention relates to a machine used for piercing a taphole for a shaft furnace related to the so-called "lost rod" method used for piercing a taphole for a shaft furnace used in the production of steel. The lost rod method comprises blocking the taphole with taphole clay. Before the taphole clay has fully hardened, a metal rod is driven into and through this clay to a desired depth into the shaft furnace. At the appropriate time, the metal rod is extracted to open the taphole using a piercing rod machine. In accordance with this invention, such a piercing rod machine comprises a mounting which can be oriented in front of the shaft furnace wall in a working position in the extension of the axis of the taphole, a carriage which can be displaced along the mounting and a drive means to drive the carriage along the mounting.
The prior art teaches how to use conventional piercing machines, designed for working with a drill bit, for piercing tapholes with the lost rod method. These machines include a chuck fitted with a coupling means for the rod along with a powerful two-directional pneumatic hammer for supplying the force necessary for inserting and extracting the piercing rod.
A powerful pneumatic hammer of the type used on these piercing machines has its problems. The hammer exerts considerable stresses and vibrations on the equipment and, particularly, on the coupling means connecting the piercing rod to the working member resulting in rapid wear of the coupling means. In addition, the pneumatic hammer is extremely noisy and often does not conform to the ever-stricter standards aimed at reducing the noise level in the industrial environment. These disadvantages of the pneumatic hammer make it desirable to eliminate the percussion (or noise level) of the hammer during insertion and extraction of the piercing rod.
The prior art teaches a method for extracting the piercing rod using a powerful drive means coupled firmly to the free end of the piercing rod. This method uses a forceful recoil movement to withdraw the piercing rod from the taphole without producing vibrations and is completely silent. This extraction method has been tried on various machines and produces entirely satisfactory results. The drive means on these machines are either jacks or hydraulic motors and use special clamps as means for coupling the drive means to the piercing rod.
Unfortunately, such a silent "forceful" solution is not available for the operation of inserting the piercing rod into the hardening taphole clay. In fact, given the dimensions of the piercing rod (a normal piercing rod has a length of 4 m and a diameter of 4 cm) a powerful axial thrust risks (1) causing the rod to buckle and (2) that the piercing rod may be permanently blocked in a position in which the rod is partially driven into the rapidly hardening clay.
A proposed method to resolve the aforementioned problems during the "forceful" insertion operation was used comprising intermediate guides fastened on the mounting and circumferentialy encircling the piercing rod at several points and to put these guides successively, in step with the advancement of the clamp toward the front of the mounting, in a position which does not hinder the forward travel of the clamp. Slidable guides were installed on the mounting. These guides are thrust forward by the forward travel of the clamp into a position at the front of the mounting. However, this solution had certain problems. For one thing, these sliding intermediate guides constitute very vulnerable elements. Considering the rough working conditions to which a piercing machine is subjected, the guides risk becoming blocked in their guide rails and, thus, constitute an obstacle to the forward travel of the clamp. In addition, the arrangement of a parked position at the front of the mounting for these intermediate guides not only constitutes an obstruction problem at the front of the mounting, but also subjects these intermediate guides to the splashes coming from the jet of molten metal from the taphole. Also, practical experience has shown that the buckling of the piercing rod between two successive supports is not totally precluded. A piercing machine which makes it possible to drive a piercing rod into the semi-hardened taphole clay using a powerful force to the free end of the piercing rod without buckling as well as resolving the other problems discussed is required.